sending TCP reset

Hello all you readers,
For a student project, I'm going to develop a simple application which stay in the gateway and send TCP reset to live connections which matches to my criteria. The program should work in sniffer mode. I had some R&D around snort and pcap but want to know if anybody has experiences in this issue. please guide me.

Hello all you readers,
For a student project, I'm going to develop a simple application which stay in the gateway and send TCP reset to live connections which matches to my criteria. The program should work in sniffer mode. I had some R&D around snort and pcap but want to know if anybody has experiences in this issue. please guide me.

Cheer ya all.
Sindy

For a clue I'm looking for a working code such as snort but snort is really complicated. You know any simple application that performs all or parts of the subject?